1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a high-speed wavelength selectable optical source and a method thereof, and more particularly to a high-speed wavelength selectable optical source and a method thereof which can selectively output a light having one wavelength among several wavelengths generated from a multimode optical source as an optical source for wavelength selectable optical communications.
2. Description of the Related Art
In constructing a communication network using light, one technology generally used to heighten the throughput and to achieve an effective network application is a WDM (Wavelength Division Multiplexing) transmission technology. This WDM transmission technology has already been researched by many research institutes and has already been introduced in networks provided by some long-distance communication service providers.
The WDM is a technology for carrying several kinds of data on one optical fiber using light having different wavelengths, and refers to an optical transmission method that improves communication capacity and speed.
The optical communication is superior to other communication methods in performing communications in a very wide frequency range. The WDM transmission method starts with the intention of utilizing such a wide frequency band to the maximum, and uses wavelength ranges of 1310 nm and 1550 nm. A recent WDM transmission method provides that several channels for carrying signals thereon are arranged at predetermined intervals of wavelength in the vicinity of the wavelength range of 1550 nm, and then optically multiplexed so that they are transmitted through one optical fiber. On the receiving side, the respective channels are demultiplexed by wavelength and then separately used.
Such optical sources for optical communications generally used may be a Light Emitting Diode (LED) and a laser diode, and for the WDM transmission, a plurality of single-wavelength optical sources that oscillates in different wavelengths is necessarily required.
The laser diode is composed of a semiconductor chip having one PN junction, one side surface of which constitutes a reflecting mirror. If current is applied to the PN junction, holes having a positive charge and electrons having a negative charge are coupled together to cause stimulated emission of light having a plurality of wavelengths to occur.
As described above, the optical source that emits light having a plurality of wavelengths is called a multimode optical source, and the optical source that outputs only the light having a wavelength selected among the plurality of wavelengths and attenuates the light having the remaining wavelengths is called a single-mode optical source. Further, a tunable optical source can output the light having a wavelength optionally selected among the plurality of wavelengths and change the selected wavelength as well.
As conventional tunable optical sources, there are an external cavity laser, a tunable Distributed FeedBack (DFB) laser disclosed in U.S. Pat. No. 6,754,243, etc.
The external cavity laser requires a stabilizing circuit for stabilizing the wavelength after the wavelength is tuned, and this causes the wavelength tunable speed to be lowered. Also, an unwanted transient effect may occur while the wavelength is tuned to a specified wavelength. Additionally, the tunable speed is lowered by the mechanical movement of an external mirror.
In the same manner, the tunable DFB laser requires several optical sources called a DFB laser array, and has a low tunable speed since it uses a Micro Electro-Mechanical System (MEMS) switch. Further, it requires an accurate control for connecting the MEMS switch and the laser diode.
Accordingly, an optical source which does not require plural optical sources, which has an improved wavelength tunable speed and which is easy to control is needed.